152 UTILITARIAN DOCTRINE, HOW FAR TRUE : [CHAP. VI. 



Natural selection cannot possibly produce any modification in 

 a species exclusively for the good of another species; though 

 throughout nature one species incessantly takes advantage of, and 

 profits by, the structures of others. But natural selection can 

 and does often produce structures for the direct injury of other 

 animals, as we see in the fang of the adder, and in the ovipositor 

 of the ichneumon, by which its eggs are deposited in the living 

 bodies of other insects. If it could be proved that any part of the 

 structure of any one species had been formed for the exclusive 

 good of another species, it would annihilate my theory, for such 

 could not have been produced through natural selection. Although 

 many statements may be found in works on natural history to 

 this effect, I cannot find even one which seenu to me of any 

 weight. It is admitted that the rattlesnake has a poison-fang for 

 its own defence, and for the destruction of its prey; but some 

 authors suppose that at the same time it is furnished with a rattle 

 for its own injury, namely, to warn its prey. I would almost as 

 soon believe that the cat curls the end of its tail when preparing 

 to spring, in order to warn the doomed mouse. It is a much 

 more probable view that the rattlesnake uses its rattle, the cobra 

 expands its frill, and the puff-adder swells whilst hissing so loudly 

 and harshly, in order to alarm the many birds and beasts which 

 are known to attack even the most venomous species. Snakes 

 act on the same principle which makes the hen ruffle her feathers 

 and expand her wings when a dog approaches her chickens ; but 

 I have not space here to enlarge on the many ways by which 

 animals endeavour to frighten away their enemies. 



Natural selection will never produce in a being any structure 

 more injurious than beneficial to that being, for natural selection 

 acts solely by and for the good of each. No organ will be formed, 

 as Paley has remarked, for the purpose of causing pain or for 

 doing an injury to its possessor. If a fair balance be struck 

 between the good and evil caused by each part, each will be found 

 on the whole advantageous. After the lapse of time, under 

 changing conditions of life, if any part comes to be injurious, it 

 will be modified ; or if it be not so, the being will become extinct 

 as myriads have become extinct. 



Natural selection tends only to make each organic being as 

 perfect as, or slightly more perfect than, the other inhabitants of 

 the same country with which it comes into competition. And we 

 eee that this is the standard of perfection attained under nature. 

 The endemic productions of New Zealand, for instance, are perfect 

 one compared with another ; but they are now rapidly yielding 

 before the advancing legions of plants and animals introduced 

 t:om Europe. Natural selection Avill not produce absolute per- 

 fection. <ior do we always meet, as far as we can judge, with this 



